In a continuously variable transmission, a ratio varying unit (“variator”) is used to provide a continuous variation of transmission ratio. The variator is coupled between the transmission input and the transmission output via gearing and one or more clutches. In the variator, torque is transmitted by frictional engagement of variator discs and corresponding rollers separated by a traction fluid. In toroidal-type variators, each input and output variator disc includes a curved, confronting contact surface that cooperate to form a toroidal void or chamber in which the variator rollers are positioned.
The variator rollers are controlled by a hydraulic piston/cylinder arrangement, which applies a force to the rollers based on a pressure difference applied to the hydraulic piston. The output torque of the variator is defined by the control piston force acting on the variator rollers. The position or contact angle of each roller on the corresponding input and output variator discs is dependent on the variator ratio, which is defined by the resulting speed ratio between the output and input discs. An endload assembly applies an axial force on the end endload disc, which in turn applies a normal force to the variator discs to ensure traction of the rollers on the corresponding discs. However, at extreme low or high variator ratio, the contact normal force applied to the rollers by the variator discs increases in proportion to the force on the roller control pistons due to the contact angle of the variator roller on the discs. Such increase in the contact normal force at extreme contact angles may result in overclamping of the rollers, reduction of variator efficiency, and/or reduction of component life.